Apparatus for sterilizing surfaces with hydrogen peroxide

ABSTRACT

An apparatus for sterilizing surfaces has a tube and a plurality of nozzles wherein a mixture of hot air and vaporized hydrogen peroxide is fed from the tube, which is heated and which includes a porous section for feeding vaporized hydrogen peroxide into hot air fed through the tube to provide a mixture of hot air and vaporized hydrogen peroxide, the mixture being fed from the tube to surfaces to be sterilized by the nozzles.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional application of application Ser. No.08/700,659 which was filed Aug. 9, 1996.

BACKGROUND OF THE INVENTION

The present invention relates to sterilizing surfaces with hydrogenperoxide and particularly with a mixture of air and gaseous hydrogenperoxide and more particularly, to apparatus for effecting the same.

The sterilisation of packaging materials with gaseous hydrogen peroxideis well known in the art. The European Patent Application PublicationNo. 0 481 361 concerns an apparatus for sterilising containers whichcomprises a nozzle as the source of liquid hydrogen peroxide and heatedair for vaporising said hydrogen peroxide. The drawback of this systemis that the use of a nozzle for introducing the liquid hydrogen peroxideleads to e tendency for blocking said nozzle, and secondly, it is moredifficult to enable uniform atomisation and a complete vaporisation whendroplets have to be vaporised. Furthermore, specific vaporisationchambers often require a high vaporisation temperature and thedecomposition rate of hydrogen peroxide can be relatively high. Finally,the apparatus of the above-mentioned patent application is complicated,which makes the maintenance and cleaning more difficult and expensive.

SUMMARY OF THE INVENTION

The aim of the present invention is to overcome the above-mentioneddrawbacks and particularly to provide a process and also to provide anapparatus for carrying out the process wherein a complete vaporisationof the aqueous hydrogen peroxide, a constant concentration of hydrogenperoxide in the vapour-phase and a minimised decomposition of hydrogenperoxide can be guaranteed.

This invention provides a process for continuously sterilizing surfaceswith a mixture of air and gaseous hydrogen peroxide wherein a stream ofhot air is fed through a feeding tube to the surfaces to be sterilised,characterized in that, the hot air is mixed with completely vaporisedhydrogen peroxide, wherein the vaporised hydrogen peroxide is diffusedfrom a porous section of the feeding tube into the hot air stream toprovide a hot air and vaporised hydrogen peroxide mixture to nozzleswhich feed the mixture to surfaces for sterilising the surfaces, saidvaporized hydrogen peroxide being obtained by forming a thin film ofliquid hydrogen peroxide in a porous tube section and by heating it,said porous tube section forming part of the hot air feeding tube anddiffusing said vaporized hydrogen peroxide into the hot air stream.

The process according to the present invention takes advantage of thefact that heat and mass transfer during evaporation are considerablyhigher when a thin film of liquid is in contact with a hot surface,compared to the above-mentioned European '361 Application technologywith evaporation of droplets in a hot air stream. Therefore, theformation of a well-spread thin film of liquid hydrogen peroxide isensured by using a porous tube.

The invention further provides an apparatus for continuously sterilisingcontainers in an aseptic filling line wherein the apparatus comprises atube and a plurality of nozzles wherein a mixture of hot air andvaporised hydrogen peroxide is fed from the tube through nozzles tosurfaces to be sterilised, wherein the tube includes a porous tubesection for feeding, directly, the gaseous hydrogen peroxide into astream of hot air, the tube being surrounded by a heating means.

DETAILED DESCRIPTION OF THE INVENTION

According to the present invention, "under surfaces" is to be understoodas any type of enclosures, such as packagings made with any type ofpackaging material, such as glass, plastic, or metal.

The normal temperature of vaporisation of hydrogen peroxide in aqueousphase is about 107° C. with approximately 35% hydrogen peroxide inweight. The vaporisation of the hydrogen peroxide is performed at atemperature of from 110 to 130° C. of the heating equipment. Thetemperature must be high enough to guarantee the vaporisation of all thehydrogen peroxide, but not too high to avoid a decomposition of said H₂O₂. Typically, the temperature of heating equipment is around 120° C.

The process according to the invention is continuous and taking inaccount the new way of vaporisation, the consumption of hydrogenperoxide can be reduced. The concentration of hydrogen peroxide is from5 to 20 mg/liter of air.

To prevent the gaseous hydrogen peroxide from condensing, the wholeapparatus is kept at a temperature of the order of 120° C. The hot airstream is generated by means of a low pressure ventilator and a simpleheat exchanger and can be easily monitored using a flow meter.

After the sterilisation step, according to the concentration of thehydrogen peroxide, condensation of said hydrogen peroxide can occur, andin this case, it is preferred to remove these residues and to have adrying air flow arriving on the sterilised surfaces at a temperature ofthe order of 120° C.

It is also preferable according to the invention to be sure that anefficient sterilisation effect can be guaranteed, and it is thereforepreferable to have means for monitoring the temperature, the hot airflow rate and the hydrogen peroxide concentration of the gaseousmixture. The hot air flow rate depends on the diameter of the feedingtube and on the number of containers which has to be sterilised on theline. Normally, the air rate is from 20 to 50 l/min per container.Concerning the hydrogen peroxide concentration, it is measured on-lineby means of a photometer or a system based on the thermal effect of acatalytic decomposition of hydrogen peroxide, wherein a small part ofthe stream of hydrogen peroxide is sucked through the measuring device(photometer or catalyst) using a small vacuum pump, which is explainedin more detail hereunder.

As already said before, it is preferred that the hydrogen peroxide istotally vaporized at the moment of mixing with the hot air.

The porous tube is a sintered metal tube, for example made fromstainless steel having pores of a diameter of 20 to 80 microns,preferably on the order of 40 microns. If the pore size is below 20microns, large pumping pressures are required for the liquid hydrogenperoxide and the pores run the risk of becoming blocked. On thecontrary, if the pore size is too great, this leads to the risk that notall the hydrogen peroxide is vaporised.

The thickness of the porous tube should be selected carefully for bestresults. In thin tubes, the contact period is not sufficient forallowing vaporisation and in tubes which are too thick, too great adecomposition of the hydrogen peroxide can occur. The best thickness isfrom 3 to 4 mm. Concerning the length, it must be sufficient to allow anadequate flow rate and evaporation of the hydrogen peroxide, leading toan efficient concentration in the stream of hot air, the optimal lengthbeing 15 to 30 cm.

The liquid hydrogen peroxide is in aqueous solution. The concentrationis not critical, but is preferably between 5 and 45%, preferably about35%. As already mentioned above, it is preferred to prevent anypossibility of condensation, for example of steam coming from the waterof the hydrogen peroxide, and the feeding tube is therefore steam heatedat a temperature to about 120° C.

In the case of an apparatus which could be operated under ultrahygienicconditions, it would be also possible to reduce the hydrogen peroxide toas low as 0; the sterilization efficiency is reduced to vegetative germsonly compared with a reduction of the thermophilic spores for hydrogenperoxide, and it necessitates a heating of the feeding tube as high as170° C.

In the device according to the invention, the feeding of the gaseoushydrogen peroxide occurs through one feeding inlet or several, dependingon the machine capacity. The diameter of the feeding tube of hot air iscorrespondingly increased.

To measure the hydrogen peroxide concentration, the apparatus comprisesfurther a photometer or a system based on the catalytic decomposition ofhydrogen peroxide.

Hydrogen peroxide shows a characteristic absorption peak at a wavelengthof 200 nm. A standard photometer is combined with a vacuum pump, whichguarantees a constant flow of the test gas through the measuring cell.To keep the test gas above the dew point, cylindrical and heatedmeasuring cells are used.

The thermal effect of the catalytic decomposition of hydrogen peroxidecan easily be measured by means of a small catalyst. A constant smallpart of the gas flows through a little catalyst that consists of aceramic wafer material that is kept at a temperature of 120° C. Due tothe exothermic decomposition of the gaseous hydrogen peroxide intooxygen and water, a significant temperature increase of the test gas canbe measured between the inlet and the outlet of the catalyst. Thistemperature increase can be exactly correlated with the hydrogenperoxide concentration.

The apparatus according to the invention gives a tubular distributionsystem for the H₂ O₂ vapour, without any valve, orifices or othercomponents, built in. The correct gas distribution to the individualsurfaces is assured by exchangeable nozzles, which can be calibrated atthe corresponding outlets, to ensure amount of gas wanted at thespecific place.

Both these control systems are appropriate for the continuous monitoringof the hydrogen peroxide vaporization quality and the sterilisationeffect during production.

An embodiment of the invention is described with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

FIG. 1 shows a schematic view of the apparatus according to theinvention.

FIG. 2 shows a cross section of a portion of the apparatus of FIG. 1.

DETAILED DESCRIPTION OF THE DRAWING FIGURES

FIG. 1 demonstrates the principle of a package sterilization by means ofthe hydrogen peroxide vaporiser which, as illustrated, includes anelongated outer surface opposed by an elongated inner surface about atube hollow which defines and thereby contains one elongated tubepassage. The liquid hydrogen peroxide, represented in FIG. 1 by alabelled box and arrow, is fed directly onto the porous tube section (4)by means of a positive pump (not shown), said peroxide being vaporisedby means of the steam jacket (3) heating the porous tube. The hot airstream, represented in FIG. 1 by a labelled box and arrow, is generatedby means of a conventional low pressure system (not shown). To preventthe gaseous hydrogen peroxide and the steam from condensation, thefeeding tube (10) is heated with a steam jacket (5). The packages (9) tobe sterilized are disposed directly under the corresponding nozzles (8)diffusing the mixture of hot air and gaseous hydrogen peroxide. Ameasuring device (6), such as a photometer, is disposed on-line viapiping (18), as illustrated, to control the concentration of thehydrogen peroxide in the line, a measured part controlled by a flowmeter (19) of the main stream being sucked through said measuring devicewith the help of a small vacuum pump (7). The nozzles (8) are alsoequipped with a steam jacket (11), avoiding therefore any risk ofcondensation in the whole sterilising apparatus.

In operation and with reference to FIG. 2, the steam jacket of thevaporizer comprises two concentric tubes (12,13), which are heated bysteam, at a temperature of 120° C., flowing through the channel (14).The liquid hydrogen peroxide, represented in FIG. 2 by a labelled boxand arrow, arriving through inlet (15) diffuses through the porous tube(4), where it is totally vaporized by the heating of tube (13), andenters the feeding tube (10) and mixes with the arriving hot air stream,represented in FIG. 2 by a labeled box and arrow, fed to and within andlongitudinally through tube (10). The vaporizer comprises further aconnecting part (16), which is necessary for allowing said vaporizer tobe disposed in the feeding tube (10). A second part (20) comprises anextension (17) for preventing the liquid hydrogen peroxide from directlydripping into the air stream. A connecting ring (21)joins the connectingpart (16) with the part (20). Taking in account the presence of thesteam jackets (5,11), no condensation occurs, and also with reference toFIG. 1, the mixture of air and hydrogen peroxide flows through thefeeding tube (10) at the nozzles (8) to sterilise the containers (9),which are then ready to go to the drying stage (not shown) and finally,under the aseptic filling nozzle. Three seconds are normally necessaryfor the sterilization of each container.

In the case of an apparatus operating with several inlets (15), thepresence of the extension (17) is no more useful.

EXAMPLE

The apparatus of FIGS. 1-2 is used with hydrogen peroxide at aconcentration of 35% and operating with a steam jacket at 120° C. forthe sterilization of containers (volume of 200 ml) for asepticapplications. A concentration of the hydrogen peroxide in the gaseousmixture of 10 mg/liter of air is used.

The nozzle (8) operates at 30 l/min. to reach a decimal reduction of 5 Dwith Bac. subtilis, var. globigii and exposure time of 3 sec.

We claim:
 1. An apparatus for sterilizing a surface wherein theapparatus comprises:a tube structure which comprises an elongated outersurface opposed by an elongated inner surface about a tube hollow todefine one hollow elongated tube passage for passage of hot air andwhich comprises, for a portion of its length, a tube section which isporous for diffusing hydrogen peroxide fed to the outer surface and intothe passage via the inner surface for feeding vaporized hydrogenperoxide into the passage for mixture with hot air passed in the passagepast the porous section; means for heating the tube structure to atemperature for vaporizing liquid hydrogen peroxide; a plurality ofnozzles connected with the tube structure at a position for receiving,from the passage, a mixture of hot air and vaporized hydrogen peroxidepassed in the passage past the porous section for feeding the mixturefrom the tube structure to surfaces for sterilizing the surfaces; andwherein the elongated passage is the only elongated passage containedwithin the tube structure.
 2. An apparatus according to claim 1 whereinthe means for heating the tube structure comprises a jacket whichsurrounds the porous tube section for supplying heat to the porous tubesection.
 3. An apparatus according to claim 1 wherein the tube structurecomprises a further section which extends from the porous tube sectionand wherein the nozzles are connected to the further section and whereinthe means for heating the tube structure comprise a jacket whichsurrounds the porous tube section and a jacket which surrounds thefurther section for supplying heat to the porous tube section and thefurther tube section.
 4. An apparatus according to claim 1 or 2 or 3further comprising a jacket positioned for supplying heat to eachnozzle.
 5. An apparatus according to claim 1 or 2 or 3 furthercomprising means for generating hot air and for feeding the hot airgenerated to the tube structure for passing the hot air in the passagepast the porous tube section to obtain the mixture of the hot air andvaporized hydrogen peroxide.
 6. An apparatus according to claim 4further comprising means for generating hot air and for feeding the hotair generated to the tube structure for passing the hot air in thepassage past the porous tube section to obtain the mixture of the hotair and vaporized hydrogen peroxide.
 7. An apparatus according to claim1 wherein the porous tube section is comprised of sintered metal.
 8. Anapparatus according to claim 1 wherein the porous tube section has poreshaving a diameter of from 20 microns to 80 microns.
 9. An apparatusaccording to claim 7 or 8 wherein the porous section has an outersurface to inner surface thickness of from 3 mm to 4 mm.
 10. Anapparatus according to claim 1 further comprising a photometer connectedwith the tube at a position for measuring hydrogen peroxideconcentration in the hot air and vaporized hydrogen peroxide mixture inthe tube.
 11. An apparatus according to claim 1 wherein the meanscomprising a thermal catalytic decomposition catalyst connected with thetube at a position for measuring hydrogen peroxide concentration in thehot air and vaporized hydrogen peroxide mixture in the tube.